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Hi Rob

I guess it depends on what's going on on your system. I can understand that
when something gets written to a disk then the parity bits have to be
written in that set so that would mean that the other disks in the same
parity set might be slightly busier than other disk not involved in the
parity stripe for that instant.

That (maybe) goes partway to explaining some of what you are seeing as the
disks you showed are striped differently. The busiest ones held the parity
bit and maybe the other disk was the one written to "that instant". V5R4
does allow you to build the RAID sets based on capacity or usage and stripes
the disks differently based on this.

I don't know how system i makes decisions about how much data to write to a
disk set before writing it to another disk set. This would probably skew
disk activity over the shorter time frame I guess. It's certainly been my
experience that over a longer time frame - say 3-5 minutes - the disks in
any given ASP look about the same % busy.

Worst case I've ever seen was a system where a disk was added to an ASP and
then before any balancing was done a library was restored. Entire library
ended up on one physical disk. Every time a heavy batch job or save was run
against on that library the system used to freak out with that one arm going
to 100% busy.

Regards
Evan Harris

-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of rob@xxxxxxxxx
Sent: Thursday, 6 December 2007 8:04 a.m.
To: Midrange Systems Technical Discussion
Subject: RE: STRASPBAL

All drives in the same ASP.

Let's try a new elapsed time.
Elapsed time: 02:46:35
Ok, that could be the difference. Now the %busy only spreads out from 2
to 9%. Now the raid sets are only off by a percentage or two.

I am still thinking that I shouldn't be seeing those bursts that I saw
earlier. Granted, the duration may balance out but why should I get
bursts only on a particular raid set?

Rob Berendt

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